2 CHEMICAL AGENTS AND PROTOPLASM [Ch. I 



certain indirect means for determining its constitution. Since 

 death is due to chemical change, we ought to determine what 

 substances are fatal poisons to protoplasm ; and since every 

 activity of protoplasm is a chemical process, we ought to 

 study the modifications of these processes by the action of 

 various chemical reagents. 



In studying the behavior of protoplasm in the presence 

 of various reagents, we shall make use especially of observa- 

 tions upon Protista, sexual cells, and tissue cells. In cases 

 where sufScient observations on isolated plant or animal cells 

 are wanting, use will be made of observations upon Metazoa. 



At the outset, attention should be called to the necessity 

 of a more quantitative study of the subject. A quantitative 

 study demands, especially, a careful noting of the conditions 

 of the experiment ; for the various physical conditions under 

 which the reagent is applied modify the result. Thus, it has 

 been shown, for example, by Richet ('89, p. 212) that with 

 various poisons the toxic dose diminishes in amount with the 

 elevation of the temperature of the body. 



1. Oxygen. — It is almost certain that no protoplasm can 

 long survive in the absence of oxygen. Apparent exceptions 

 are found in the case of the anaerobic bacteria, some of which 

 are killed in the presence of free oxygen, but multiply rapidly 

 when the oxygen supply is cut off. It has been suggested that, 

 in the case of these and some other parasitic organisms, oxygen 

 is derived from the breaking down of O -containing compounds 

 in the nutritive medium. (Cf. Loew, '91, p. 760.) 



The effect of diminished oxygen upon protoplasm is described 

 by Clark ('89, pp. 370, 371) and by Dbmook ('94, p. 191). 

 Clark determined the minimum oxygen pressure necessary for 

 the vital movements of the plasm odia of Myxomycetes and the 

 protoplasm of plant hairs and tissue cells. This he found to 

 range from 1 mm. (plasmodia of Myxomycetes) to 3 mm. (leaf 

 hairs of Urtica) of mercury. 



DBMOOii * subjected Tradescantia stamen hairs, in water, to a 



* In studying the effect of a vacuum, Demook employed a piece of apparatus 

 constructed essentially on the plan of an Engelmann's chamber. This consists 

 of a box whose top is a centrally perforated metallic diaphragm and whose 

 bottom is a circular glass. The vertical walls consist of an outer cylinder, at 



